1. Field of the Invention
The present invention relates to a plate welding structure for overlapped plates to be welded by, for example, laser and to a head suspension incorporated in, for example, a hard disk drive of an information processing device such as a personal computer.
2. Description of Related Art
An example of a plate welding structure is disclosed in Japanese Unexamined Patent Application Publication No. 2002-133809. FIGS. 13 to 15 explain such a conventional plate welding structure, in which FIG. 13 is a partly broken side view showing part of a head suspension 101 before welding, FIG. 14 is an enlarged sectional view showing essential part of FIG. 13, and FIG. 15 is an enlarged sectional view showing the same part after welding.
The head suspension 101 has a load beam 103 and a base plate 105.
The load beam 103 includes a rigid part 107 and a resilient part 109 and serves to apply load on a head slider (not shown) that is arranged at a front end of the load beam 103. The resilient part 109 is made of a resilient plate 111. The resilient plate 111 has a base that is held between the base plate 105 and a reinforcing plate 113 and is laser-welded and fixed between them. The laser welding is carried out by forming small holes 115 in, for example, the reinforcing plate 113 as shown in FIGS. 13 and 14. A laser beam is aimed at each small hole 115 and forms a weld part W shown in FIG. 15.
The base plate 105 is provided with a boss 117 to be fitted to an arm of a carriage.
The small holes 115 formed in the reinforcing plate 113 allow the overlapped base plate 105, resilient plate 111, and reinforcing plate 113 to be welded together with a laser beam of reduced energy. Reducing the energy of a laser beam is effective to suppress the generation of spattered matter.
Emitting a laser beam to the small hole 115, however, needs the precision positioning of the reinforcing plate 113 and laser beam. This puts a limit on mass production.
To solve the problem, the small holes 115 may be enlarged so that a laser beam is easily aimed at each small hole. However, excessively enlarging the small holes 115 results in making each small hole disproportionate to the weld part W as shown in FIG. 16. In this case, even if the strength of the weld part W is sufficient, a gap 119 may be formed between the weld part W and the hole 115 to make it difficult to distinguish a defective weld from an acceptable weld by eye.
In addition, the presence of the gap 119 may catch air that is hardly removable even with an inert gas such as a nitrogen gas blown thereto at the time of laser welding. Then, the air with a laser reaction will change color around the gap 119.
If no small holes 115 are formed for laser welding, a laser beam of increased energy must be employed. This results in generating spattered matter and deforming the reinforcing plate 113 and the like during the welding.